Play stops on speakers when changing music on another

There are two scenarios that keep occurring since adding additional speakers this week. 

1. When I have a group that is playing music and start music on a separate speaker via the app not part of that group, the group music stops
2. Similarly, when I have a group that is playing music and start music on a separate speaker via Sonos Voice Control, the group music stops

It would appear that it doesn’t seem to matter whether the music already playing is coming from a group or an individual speaker, in both cases it stops and I have to play about in the app to get it so that different music is playing from different zones.

This doesn’t seem right or feel like good user experience. Can someone expand on this and whether there is an issue here?

In my set up I have an Era 100 which is in our loft, an Era 300 which is in our dining room, a Beam gen2 and mini sub in the lounge and a Move 2. Music is playing from Spotify which I have added as a service.

Thanks